For ramjets you slow down the air flow so that the combustion has time to complete. Slowing down the air flow creates extreme heat. But that heat is not lost since it contributes to the energy of the combustion.
But at some point at about Mach 5.5 that heat becomes to great and it can not be recovered, resulting in efficiency loss.
I don’t get that. According to Carnot’s 2nd Law the higher heat means it more efficiency can be converted back and forth between heat and energy of motion.
So why do ramjets lose efficiency at the higher Mach numbers?
In: Engineering
You have to slow down the air before it gets into the combustion chamber, and heating up the part that slows the air down doesn’t help anyone. Plus it gets really hard to do because shockwaves mess up any sort of smooth airflow you try and set up
you can not do that and do the combustion with not slow air, but then it’s a scram jet and not a ram jet
Shockwaves are extremely entropic…there are huge loses through the shock and it gets worse as you go faster. You don’t *want* heat coming into the combustor, you want pressure. Heat is just an undesired side effect. Then you want to *add* heat with fuel. If you’re already crazy hot because of ram compression it limits how much heat you can add in fuel because the maximum temperature is limited by what the engine material can withstand. So the faster you go the less fuel you can add and the more losses you have in the inlet so your efficiency drops off.
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